Rubber crawler

ABSTRACT

A rubber crawler which is mounted on a continuous chain tread traveling device, such as an agricultural working vehicle, a civil engineering machine, a construction machine or a transportation vehicle, and designed to improve durability in the connecting section of a tensile strength body embedded therein. A plurality of tensile strength bodies ( 5 ) paralleled and arranged in a row widthwise of the rubber crawler ( 1 ) along the circumferential direction of the rubber crawler are divided into two along the middle of the rubber crawler. In embedding the two rows of tensile strength bodies in the rubber crawler, the front ends of the opposite ends ( 5   a   , 5   b ) of the individual tensile strength bodies are abutted against each other and connected together into an endless form. Of the two right and left rows of tensile strength bodies, the position of the butt portions ( 6 ) of not less than 80% of the tensile strength bodies ( 5 ) in the connecting portion of each row of tensile strength bodies is such that the position of the butt portions ( 6 ) of adjoining tensile strength bodies ( 5 ) is shifted longitudinally circumferentially of the rubber crawler ( 1 ) with respect to the position of the butt portion ( 6 ) of a single tensile strength body ( 5 ).

TECHNICAL FILDS

[0001] The present invention relates to a rubber crawler which is mounted on an endless tread traveling device, such as an agricultural working vehicle, a civil engineering machine, a construction machine or a transportation vehicle, and especially to an improvement of a connecting section of a tensile strength body embedded therein.

PRIOR ART

[0002] A rubber crawler has been used for a traveling device of various self-running type move machines, such as an agricultural working vehicle, a civil engineering machine, a construction machine and a transportation vehicle.

[0003] As shown in FIGS. 28 and 29, the conventional rubber crawler is defined by metallic core bars embedded in a rubber crawler 17 at regular intervals along a circumferential direction of the rubber crawler and pluralities of tensile strength bodies (usually, steel codes 21 are used) arranged and embedded in the tread side (the outer peripheral side) of the core bars along the circumferential direction of the rubber crawler. Here, FIG. 28 is a perspective view showing an example of the conventional rubber crawler. FIG. 29 is a perspective view in an important part section showing the example of the conventional rubber crawler, and 22 is a departure-preventing guide and 20 is a lug.

[0004] Usually, ground on which an agricultural working vehicle (such as a combined harvester or a tractor), an agricultural transportation vehicle and a snow vehicle run is made of clayey soil or snow, and is comparatively flat. Therefore, in the rubber crawler used for these working vehicles, connecting sections of the tensile strength bodies embedded therein rarely damage.

[0005] Besides, since the civil engineering machine or the construction machine, such as a mini shovel or a power shovel, runs on an irregular ground, earth and sand, gravel, etc. are bitten into the traveling device. Therefore, unusual tension and big driving force occur to the rubber crawler frequently, and the connecting sections of the tensile strength bodies of the rubber crawler are sometimes damaged. However, since the mini shovel or the power shovel is a machine of the main work of digging, this matter has rarely taken serious trouble up to the present.

[0006] Moreover, though the transportation vehicle, such as a carrier dump, mainly purposes running on coarse roads, such as an irregular ground, it only moves. Therefore, since earth and sand, gravel, etc. are not bitten into the traveling device, troubles rarely occur in the connecting sections of the tensile strength bodies of the conventional rubber crawler.

[0007] However, though a skid-steer or a bulldozer is a machine for working in the place similar to the transportation vehicle, they are used for pushing the earth and sand or dipping up them, and therefore they need big driving force. Besides, since they frequently run inside earth and sand or gravel in zigzag, earth and sand are easily bitten into the traveling device as well as the mini shovel or the power shovel. Accordingly, since the connecting sections of the tensile strength bodies of the rubber crawler are damaged in many cases, troubles are caused. The troubles occur especially in the travelling device with a sprocket or an idler or a rolling-wheel with small diameter of winding. Besides, the troubles sometimes occur in the travelling device without an idler-spring even the mini shovel.

[0008] Up to this time, a steel code is most generally used as a tensile strength body. The most popular connecting technique of steel codes is an end overlapping method (superposition method).

[0009] FIGS. 30 to 32 show the connecting section of the rubber crawler by the conventional end overlapping method, respectively. FIG. 30 is an important part perspective view. FIG. 31 is a sectional view taken on line X-X in FIG. 30, and FIG. 32 is a sectional view taken on line Y-Y in FIG. 30. Pluralities of steel codes 21 are arranged in a belt-shaped, pile up on their ends each other, and are connected through an adhesive rubber layer 23.

[0010]FIG. 33 is a schematic view showing a forming step that a rubber crawler is connected, and FIG. 34 is a sectional view showing the state inside a connecting form mold.

[0011] Usually, in order to manufacture an endless rubber crawler, first of all a long belt-shaped main body is formed by vulcanizing uncured rubber, core bars and steel codes with a press mold so that the steel codes extend from both ends of the main body. Then, the core bars and the uncured rubber are inserted into a press mold for connecting as piling up steel code layers arranging pluralities of steel codes in the belt-shaped, and vulcanization molding is carried out. Thus, a rubber crawler is formed.

[0012] The overlapping length L₀ of a steel code (superposition of a rubber crawler thickness direction) is usually determined by the following calculation under choosing necessary abilities suitably.

[0013] A shearing breaking load (F₀) of an overlapping section of a steel code is expressed with Formula 1, wherein an overlapping length of a steel code is set to L₀ [mm], a width of a steel code row to h [mm], a shearing breaking load per unit area to a f₀[N/mm²], and the shearing breaking load of a connecting section to F₀ [N].

[0014] Formula 1;

F ₀ =L ₀ ×h×f ₀

[0015] However, usually, since a safety factor is taken into consideration, the overlapping length in the conventional rubber crawler is calculated with Formula 2. The safety factor is set to S, and breaking strength of a steel code to F₁.

[0016] Formula 2;

L₀ >F ₁ ×S/(h×f ₀)

[0017] However, while a connection by the end overlapping method has a very convenient workability and a good efficiency, there are limits in improving running possible time due to improving durability of the connecting section of a steel code even if the overlapping length thereof is lengthened. Besides, its use is also restricted.

[0018] As shown in FIGS. 30 to 32, the overlapping section of a steel code (which the opposite ends of the steel codes are piled up) of the rubber crawler is formed so as to hold adhesive rubber between two layers of steel codes. When the overlapping section coils around the idler or the sprocket of the driving device, the steel codes of the outer circumferential side (tread side) of two layers can not coil smoothly unless they are longer than ones of the inner circumferential side (rolling wheel side). However, since the steel codes hardly extend and are hardly compressed, the adhesive rubber layer between the steel codes is converted and wound around. Therefore, shearing deformation occurs in the adhesive rubber at the opposite ends of the steel codes of the outer circumferential side or the inner circumferential side of the overlapping section.

[0019] Accordingly, in addition to tension added to the steel code from the first, unusual tension caused by insertion of foreign materials or by accumulation of earth and sand is added to the overlapping section of a steel code in the connecting section of the rubber crawler, and the shearing deformation occurs in the adhesive rubber layer between the overlapped steel codes. Besides, when the overlapping section coils around the idler or the sprocket, the shearing force is repeatedly added to the adhesive rubber layer at the ends of the overlapping sections, thereby causing the shearing deformation. Therefore, since the adhesive rubber layer of the connecting section is gradually destroyed from the ends of the steel codes, durability of the rubber crawler falls down remarkably.

[0020] The above-mentioned problems are taken up in an official gazette of Japanese Patent Provisional Publication No. 109948/1997. Though countermeasures proposed therein improve an effect fairly, they are not necessarily the wisest measures.

[0021] Besides, as another method, a method for winding the steel codes endlessly is proposed in an official gazette of Japanese Patent Provisional Publication No. 1179731/1999.

[0022] However, though the connecting section is not destroyed in this method, a special endless rolling device is required. This device must be mounted on every product with a different circumference of rubber crawler. Besides, in vulcanization process, a conventional manufacturing method that the majority of rubber crawler is vulcanized and formed with a long press and the ends thereof are connected to each other by the overlapping method, can not be carried out. At least 5 to 6 times molding vulcanization are needed. Therefore, productive efficiency becomes very bad. Moreover, in order to vulcanize it at one time, a very expensive molding vulcanizer is needed.

[0023] Furthermore, there is another method, wherein the steel codes are classified into pluralities of steel code rows, and the steel code rows extending from the opposite ends are connected each other on the core bars so that the classified steel code groups may be abutted zigzag. However; according to this connection, in case of not lengthening each length of the steel codes, sufficient pulling strength can not be obtained. Therefore, the steel codes will be pull away. To solve this problem, a proposal that a shortage of the pulling strength is improved by embedding the second steel code rows in butt connecting sections is disclosed in a official gazette of Japanese Patent Provisional Publication No. 295776/1991. In addition, a proposal for improving a shortage of the pulling strength by adjusting the core bars to the butt portions, embedding rectangular auxiliary plates in a rubber elastic body and connecting these is disclosed in a official gazette of Japanese Patent Provisional Publication No. 283180/1992.

[0024] However, these proposals are not always throughgoing measures to durability of the connecting section.

[0025] As another connecting method, there is a mutual plug method. In the plug method, the one-side tensile strength bodies are inserted between the other-side tensile strength bodies one by one and connected to each other, forming an endless form.

[0026] However, since the workability at manufacturing is bad and working hours is long, there is a problem that manufacturing cost is expensive. Besides, there is a problem in arrangement or shape that the width of a row of the tensile strength bodies of the connecting section becomes broad compared with other sites in a widthwise of the rubber crawler. Accordingly, thus connecting method is hardly used at present.

SUMMARY OF THE INVENTION

[0027] The present invention aims to solve the above-mentioned problems, and uses the following configuration.

[0028] Pluralities of tensile strength bodies are paralleled and arranged in a row widthwise of a rubber crawler along a circumferential direction of the rubber crawler, and embedded in a rubber elastic body forming the rubber crawler as tensile strength body rows. In this case, the front edges of the opposite ends of the tensile strength bodies are abutted against each other and connected together into an endless form. The tensile strength bodies are embedded and arranged so that positions of butt portions of adjoining tensile strength bodies are shifted longitudinally circumferentially of the rubber crawler with respect to a position of a butt position of a single tensile strength body.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029]FIG. 1 is an explanatory view showing the relation between the circumference of a rubber crawler and the length of a connecting section. FIG. 2 is a graph showing the relation between the circumference of a rubber crawler and the maximum length of a connecting section.

[0030]FIG. 3 is an explanatory view showing a basic pattern of one-shift lapping of a rubber crawler. FIG. 4 is an explanatory view showing a basic pattern of two-shift lapping of a rubber crawler. FIG. 5 is an explanatory view showing a basic pattern of three-shift lapping of a rubber crawler. FIG. 6 is an explanatory view showing a basic pattern of four-shift lapping of a rubber crawler.

[0031]FIG. 7A is a perspective view of a test piece for testing pulling strength of steel codes, FIG. 7B is a plane view thereof and FIG. 7C is a side view thereof

[0032]FIG. 8 is a partially sectional view of a rubber crawler for explaining an arrangement of steel codes.

[0033]FIG. 9 is a graph showing the relation between p/d of a steel code of φ2.3 and pulling strength thereof the length of a shift lapping that the steel code breaks, respectively.

[0034]FIG. 10 is a graph showing the length of a shift lapping that the pulling strength corresponding to the diameter of a steel code becomes equivalent to tensile strength thereof FIG. 11 is a graph showing the relation between the number of shift lappings corresponding to the diameter of a steel code and the length of a connecting section of a rubber crawler.

[0035]FIG. 12 is a partially perspective plane view of the first example of the invention.

[0036]FIG. 13 is a partially perspective view showing an arrangement of steel codes in the connecting section of the first example of the invention, FIG. 14 is a sectional side view, and FIG. 15 is an enlarged view in important part.

[0037]FIG. 16 is a perspective view showing the state that tensile strength bodies are arranged inside a rubber crawler.

[0038]FIG. 17 is a partially perspective plane view of the second example of the invention.

[0039]FIG. 18 is a partially perspective plane view of the third example of the invention.

[0040]FIG. 19 is a partially perspective plane view of the forth example of the invention.

[0041]FIG. 20 is an explanatory view showing an arrangement of butt portions of steel codes of the forth example in FIG. 19.

[0042]FIG. 21 is a partially perspective plane view of the fifth example of the invention.

[0043]FIG. 22 is a partially perspective plane view of the sixth example of the invention.

[0044]FIG. 23 is an explanatory view showing an arrangement of butt portions of steel codes of the sixth example in FIG. 22.

[0045]FIG. 24 is a partially perspective plane view of the seventh example of the invention.

[0046]FIG. 25 is a perspective view of the eighth example of the invention.

[0047]FIG. 26A is a partially perspective plane view of the eighth example in FIG. 25.

[0048]FIG. 27 is a side view showing a bending tester.

[0049]FIG. 28 is a perspective view showing an example of a conventional rubber crawler, and FIG. 29 is a sectional perspective view in important part showing an example thereof.

[0050]FIG. 30 is a perspective view in important part showing a connecting section of a conventional rubber crawler by an end overlapping method, FIG. 31 is a sectional view taken on line X-X, and FIG. 32 is a sectional view taken on line Y-Y.

[0051]FIG. 33 is a schematic view showing a forming step to connect a rubber crawler in an endless form.

[0052]FIG. 34 is a sectional side view showing the inside of a connecting forming mold.

[0053]FIG. 35 is a paragraph showing test result of rubber crawlers used in a flexing fatigue test.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0054] The configuration of a rubber crawler of the present invention is as follows. Pluralities of tensile strength bodies are paralleled and arranged in a row widthwise of the rubber crawler along the circumferential direction of the rubber crawler, and embedded in a rubber elastic body. In this case, the front edges of the opposite ends of the individual tensile strength bodies are abutted against each other and connected together into an endless form. The front ends of the tensile strength bodies overlap each other so that the positions of the butt portions of adjoining tensile strength bodies are shifted longitudinally circumferentially of the rubber crawler with respect to the position of the butt position of a single tensile strength body. According to this, the rubber crawler can obtain pulling strength bearable to driving force of a traveling device and a certain amount of unusual load.

[0055] The positions of the butt portions of the front edges of both ends of the adjoining tensile strength bodies are preferably shifted so that the pulling strength of each tensile strength body corresponds to tensile strength thereof And the pulling strength and the tensile strength of the tensile strength bodies are made into intensity bearable to the driving force of the traveling device and a certain amount of unusual load.

[0056] Then, the position of the butt portion of a single tensile strength body and the positions of the butt portions of its adjoining tensile strength bodies are shifted along the circumferential direction of the rubber crawler. In the adjoining tensile strength bodies, it is preferable that a shift lapping length (an overlapping length), which the tensile strength body extending from one side of the circumferential direction of the rubber crawler overlaps with the tensile strength body extending from the other side, is more than the length satisfying the relation that the pulling strength corresponds to the tensile strength. However, what is necessary is just to make total shift lapping length into what can obtain total pulling strength satisfying a relational expression shown in Formula 3. Here, Formula 3 shows that a total PS of the pulling strength of the tensile strength bodies whose opposite front ends are paralleled and arranged in a row widthwise of the rubber crawler and overlap each other becomes 80% or more of the total tensile strength of the tensile strength bodies subtracted the number CN of the butt portions in which the most many butt portions 6 exist within an interval of core bars from the number TN of all tensile strength bodies arranged in a row. There is no problem even if amounts of the tensile strength and the pulling strength get mixed up in a part of tensile strength bodies. Here, Tb is the tensile strength of a single of tensile strength body.

[0057] Formula 3;

PS≧(TN−CN)Tb×0.8

[0058] Since the front edges of the opposite ends of the tensile strength bodies are abutted, in a sprocket (driving wheel) and an idler (compensating wheel) winding section, there is no place between the tensile strength bodies to cause such big shearing deformation as occurs in the connecting section due to the conventional end overlapping method. Besides, the positions of the butt portions of the adjoining tensile strength bodies are shifted in the circumferential direction of the rubber crawler, thereby enabling to making the shift lapping length into the length such as obtaining the pulling strength bearable to the driving force of the travelling device and a certain amount of unusual load. Thus durability (fatigue resistance) against repeat curvatures in the sprocket and the idler winding section improves. Therefore, even if unusual tension increases, the connecting sections of the tensile strength bodies are not easily destroyed. Besides, durability of the connecting sections improves, thereby enabling to forming a reliable rubber crawler.

[0059] Besides, it is preferable that all the tensile strength bodies are embedded in such an arrangement as each position of the butt portions of the adjoining tensile strength bodies is shifted longitudinally circumferentially of the rubber crawler with respect to the position of the butt portion of a single tensile strength body. However, even if such tensile strength bodies are 80% among all, it is possible to obtain the pulling strength bearable to the driving force of the travelling device and a certain amount of unusual load.

[0060] Moreover, it is preferable that each position of the butt portions of the tensile strength bodies is shifted circumferentially of the rubber crawler so as not to agree with the positions of the butt portions of the other tensile strength bodies. In this case, all the butt portions are not set to the same position in rubber crawler width-of-face directional vision.

[0061] Since the butt portions of the tensile strength bodies is the most inferior in durability, the connecting sections improves in durability by not centralizing the portions with inferior durability on one place.

[0062] Usually, a rubber crawler is made into an endless form by using a press molding device or a press molding shown in FIG. 33.

[0063]FIG. 1 is an explanatory view showing the relation between the circumference of a rubber crawler and the length of a connecting section in a rubber crawler connecting process.

[0064] Numeral 1 ₁ is the possible maximum length of a connecting section, and 1 ₂ is the length of an end of a long main body of a rubber crawler inserted in a connecting mold to prevent an interval aberration. Numeral 1 ₃ is the length of a bent portion of the long main body in connecting, in vulcanizing, and in molding. Numeral 1 ₄ is the length of the connecting mold. Besides, 1 is a rubber crawler, 15 is an upper mold of the connecting mold, and 16 is a lower mold thereof.

[0065] The rubber crawler is correlated with the size (weight) of a machine in the circumference, the width, the thickness and the interval. Therefore, the length 1 ₂ and the length 1 ₃ are variables almost proportional to the circumference L of the rubber crawler excepting a unique case.

[0066]FIG. 2 shows the relation between the circumference of an actual rubber crawler and the maximum length 1 ₁ of a connecting section. The relation is expressed by Formula 4.

[0067] Formula 4;

1 ₁=19L/64−470

[0068] Accordingly, the maximum length 1 ₁ of a connecting section of various rubber crawlers is restricted to the circumference L, as shown in FIG. 2 and Formula 3. Hence, the invention provides a durable connecting method in the restricted length.

[0069] Representative examples of a basic pattern of the connecting method of the invention are shown in FIGS. 3 to 6, respectively. In these examples, a tensile strength body is a steel code. FIG. 3 shows a basic pattern of one-shift lapping, FIG. 4 shows a basic pattern of two-shift lapping, FIG. 5 shows a basic pattern of three-shift lapping, and FIG. 6 shows a basic pattern of four-shift lapping. In the figures, 5 ₁ to 5 ₅ are steel codes, 8 ₁₋₂ to 8 ₄₋₅ are shift lapping portions between steel codes, 6 is a butt portion of the end of a steel code, and L_(S) is a shift lapping length.

[0070] In every basic pattern, shift lapping portions 8 share a load of the connecting section. In FIG. 3, one-shift lapping portion 8 ₁₋₂ is constituted from two steel codes 5 ₁ and 5 ₂, and connecting efficiency thereof is set to one-half. In the pattern of FIG. 4, two-shift lapping portions 8 ₁₋₂, 8 ₂₋₃ are constituted from three steel codes 5 ₁, 5 ₂ and 5 ₃, and connecting efficiency thereof is set to two-thirds. It is set to three-fourths in FIG. 5, and four-fifths in FIG. 6, respectively.

[0071] Besides, in a practical rubber crawler, tensile strength bodies may be naturally arranged by using not only basic patterns but also deformation patterns, combination patterns, etc. It is possible to increase connecting efficiency of each shift lapping method.

[0072] A shift lapping length (L_(S)) of a connecting section of an ideal tensile strength body (steel code) is usually designed as follows.

[0073]FIGS. 7A to 7C show a test piece 11 that examines pulling strength of a steel code. Here, the pulling strength is an intensity that two steel codes 5 a in “a” direction are fixed, a steel code 5 b in “1” direction is pulled toward an arrow direction, and adhesive rubber 7 between the steel codes is destroyed. Thus the steel codes come off.

[0074] Pulling strength per unit length of a specific steel code, a shift lapping length thereof and tensile (rupture) strength thereof are respectively set to f_(S) [N/mm], L_(S) [mm] and Th [N]. When Formula 5 is satisfied, rubber portion is never damaged (the steel code is never pulled) even if the steel codes rupture.

[0075] Formula 5;

L _(S) ×f _(S) >Tb

[0076] The steel codes embedded in the rubber crawler transmit the driving force, which is received from the sprocket of the travelling device to the core bars, to the whole rubber.crawler, thereby moving the main body of the machine. Besides, since the steel codes are bonded to the core bars through adhesive rubber, the driving force is transmitted from the core bars to each steel code therethrough.

[0077] A rubber crawler is usually designed in consideration of conditions, such as the weight of a machine and driving force of a travelling device. The shape and the size of a core bar are also designed similarly. Here, the steel codes receive unusual tension many times as much as the driving force simultaneously with transmitting it from the core bars to the whole rubber crawler. The unusual tension occurs because foreign materials are bitten between the travelling device and the rubber crawler. Therefore, since the steel codes need arranging within the limited place of the core bars, an arrangement thereof cannot but become dense.

[0078] When an arrangement of the steel codes becomes dense, a space between a steel code and a steel code becomes narrow. Therefore, when pulling force is added to the steel codes of the connecting section, shearing force will be concentratively added to the adhesive rubber between the steel codes.

[0079]FIG. 8 is a partially sectional view of a rubber crawler for explaining an arrangement of steel codes in the rubber crawler.

[0080] When an outer diameter and an arranged interval of steel codes are respectively set to “d” and P, P/d is in about 1.1 to 1.5. When the steel codes 5 ₁ and 5 ₃ are pulled in front of the figure and the steel code 5 ₂ is pulled to the figure back side, stress concentration occurs in adhesive rubber 7 between the steel codes 5 ₁, 5 ₃ and the steel code 5 ₂. Since rubber breaking begins from this place, the pulling strength becomes low compared with the case where the steel codes are arranged non-densely. Therefore, what the steel codes are arranged densely needs to lengthen a shift lapping length compared with the non-dense case.

[0081]FIG. 9 shows the relation between the pulling strength to P/d of a steel code of 2.3 Φ and the shift lapping length in which the steel code breaks.

[0082] P/d of an arrangement of steel codes in a general rubber crawler is 1.22 to 1.44. When P/d is 1.3, the steel code breaks in 22 cm of a shift lapping length. On the other hand, in an arrangement that P/d is more than 2.2, it is 12.5 cm. Therefore, to obtain equal pulling strength, 1.8 times the shift lapping length is required.

[0083]FIG. 10 shows the shift lapping length that the pulling strength corresponding to the diameter of a steel code in an actual rubber crawler is equivalent to its tensile strength. When using the steel code of 2.3 Φ, if the shift lapping length is 22 cm or more, the pulling strength is more than the tensile strength. However, since the length of a connecting section is restricted by the manufacture shown previously, the pulling strength is practically set to the intensity corresponding to the tensile strength, namely, 80% or more of the tensile strength. Here, an efficient connection can be secured.

[0084]FIG. 11 shows the relation between the number of shift lappings corresponding to the diameter of a steel code and the length of a connecting section of a rubber crawler. The possible number of shift lappings in the connecting section with the restricted length is usually set to 1 to 8.

[0085] It is preferable that the tensile strength bodies which never overlap with the tensile strength body extending from the opposite direction of the circumferential direction of the rubber crawler of adjoining tensile strength bodies among the tensile strength bodies forming the butt portions within the predetermined interval of core bars from the connecting section to the adjoining core bar are arranged lest they concentrate over 25% of the whole tensile strength bodies. In this case, when there is a shortage of intensity (for example, when 25% butt portions are between the core bars), it is necessary to increase the number of tensile strength bodies more than usual, or to raise the breaking strength (increasing the number of tensile strength bodies compensating 25% shortage of intensity or using the tensile strength bodies with the high breaking strength). However; in increasing the tensile strength bodies excessively or in using the tensile strength bodies with the high breaking (tensile) strength, manufacturing costs will go up. Accordingly, these are not so desirable.

[0086] In many cases, in case the tensile strength bodies of the rubber crawler are broken by the unusual tension, they usually break within the space between the adjoining core bars. However, if the tensile strength bodies not overlapping with the tensile strength bodies extending from the opposite direction of the rubber crawler are made less than 25% of the whole tensile strength bodies, the connecting section can improve in durability.

[0087] Besides, the shortage of intensity within 25% can be compensated by increasing the tensile strength bodies or by using the tensile strength bodies with high rupture (tensile) intensity.

[0088] In this case, a range that the tensile strength bodies not overlapping with the tensile strength bodies extending from the opposite direction of the circumferential direction of the rubber crawler of the adjoining tensile strength bodies are arranged so as to be less than 25% of the whole is within all planes of projection of two adjoining core bars. Besides, it is still desirable that the arrangement is carried out within a space between two adjoining core bars.

[0089] Moreover, the butt portions of the tensile strength bodies within the predetermined interval between the core bar and its adjoining core bar are set to 40% or less in the rubber crawler connecting section. It is still desirable that they are set to 34% or less.

[0090] Furthermore, it is desirable that they are set to 25% or less within a space where the core bars are not embedded.

[0091] As mentioned in advance, since the site which the tensile strength bodies are usually break extremely exists between the adjoining core bars when unusual tension is added to the rubber crawler, the durability is improved by restricting the number of butt portions of the tensile strength bodies therebetween.

[0092] Moreover, it is preferable to arrange the positions of the butt portions of the tensile strength bodies in a plane of projection of a lug or in a plane of projection of a core bar. According to this, there is no butt portion of each tensile strength body in bending sections of the rubber crawler or in thin fractions of the tread side. Besides, while using the rubber crawler, the ends of the tensile strength bodies are prevented from breaking and exposing through the tread side of the rubber elastic body. Accordingly, the rubber crawler improves in durability.

[0093] Though a steel code is generally used as a tensile strength body, Vinylon, Nylon, Tetron, Vectlan, Kevlar, etc. can be also used. Besides, it is not limited to these.

[0094] The rubber elastic body is what reinforcing agents, such as carbon black, fillers, an antioxidant, a vulcanization accelerator, a curing agent, etc. are suitably chosen, designed and used to natural rubber or synthetic rubber (SBR, BR, IR, urethane, etc.) alone, a thing blended with combining these two or more, or a thing suitably blended high polymer resin, such as high styrene resin, etc. thereto in consideration of a working condition, required durability, a cost of a rubber crawler.

[0095] Here, the rubber elastic body used for the invention is not limited to these.

[0096] A so-called core bar less rubber crawler can be used as a rubber crawler utilizing the connecting method of the tensile strength bodies of the invention as well as the conventional rubber crawler. In the conventional rubber crawler, metallic core bars are paralleled and embedded in the rubber elastic body at a fixed interval along a circumferential direction thereof, and pluralities of tensile strength bodies are paralleled and embedded in the tread side (peripheral side) of the core bar along the widthwise of the rubber crawler. The core bar less rubber crawler is what no metallic core bars are embedded, which is mainly used for a high-speed run.

EXAMPLE

[0097] The example of the invention is explained in detail using figures.

[0098]FIG. 12 is a partially perspective plane view of the first example of the invention, FIG. 13 is a partially perspective view showing an arrangement of connecting sections, FIG. 14 is a sectional side view, and FIG. 15 is an enlarged view in important part of FIG. 13. FIG. 16 is a perspective view showing the state that tensile strength bodies are arranged inside a rubber crawler.

[0099] A rubber crawler 1 of the first example comprises a rubber elastic body 2, metallic core bars 3, lugs 4 and pluralities of steel codes 5. The core bars 3 are embedded inside the rubber elastic body 2 at a fixed interval along a circumferential direction of the rubber crawler. The lugs 4 protrude on the tread side of the rubber crawler 1. The steel codes 5 are divided into two along engaging holes 9 in the middle of the rubber crawler 1 on the peripheral side (tread side) of the core bars 3, and made into two right and left steel code rows paralleled and arranged along the widthwise of the rubber crawler 1.

[0100] A connecting section of a steel code 5 forms a butt portion 6 that the opposite ends 5 a, 5 b of the steel code 5 are abutted against each other. The positions of the butt portions 6 of adjoining steel codes 5 are shifted along the circumferential direction of the rubber crawler 1.

[0101] In FIG. 15, the positions of the butt portions 6 ₁, 6 ₂ of the adjoining steel codes 5 ₁, 5 ₂ are shited along the circumferential direction. The end 5 ₁ b of the steel code 5 ₁ and the end 5 ₂ a of the steel code 5 ₂ overlap each other along the circumferential direction, and are bonded through the adhesive rubber 7. In this case, the length from the position of the butt portion 6 ₁ of the steel code 5 ₁ to the position of the butt portion 6 ₂ of the steel code 5 ₂ is the shift lapping length L_(S). The shift lapping length L_(S) is designed by using Formula 3 under working conditions of the rubber crawler 1 or design conditions like durability so that the pulling strength may be set to an intensity corresponding to the rupture strength of the steel code 5 or more than it.

[0102] Here, this example is an example of combination arrangement with two-shift lapping.

[0103]FIG. 17 is a partially perspective plane view showing an arrangement of the butt portions 6 of the connecting section of the steel codes 5 of the second example of the invention. To each position of the butt portions 6 of the individual steel codes 5, the positions of the butt portions 6 of the other steel codes 5 are shifted longitudinally circumferentially of the rubber crawler 1, and arranged so as not to be in agreement. This example is an example of combination arrangement with three-shift lapping.

[0104] The circumference L of the rubber crawler 1 of this example is 5112 mm, and the length 1 ₁ of the connecting section is 994 mm. An outer diameter “d” of the steel code 5 is 2.3 mm, and tensile strength Tb is 5256N. Since per-unit pulling strength is 27N/mm and the shift lapping length L_(S) is 225 mm, pulling strength f_(S) is 6075N. Therefore, the pulling strength is over than the tensile strength. In ten steel codes 5 in one side of steel code rows sandwiching engaging holes 9, there are seven overlapping parts which the adjoining right and left steel codes 5 overlap with the steel codes 5 extending from the opposite direction of the circumferential direction of the rubber crawler 1 (when one steel code 5 overlaps with the adjoining right and left steel codes 5 simultaneously, since connecting efficiency is set to 1, the overlapping part is calculated to one). Hence, the total pulling strength is 7×6075=42525N. Besides, the number of the butt portions 6 within the predetermined interval of core bars with most butt portions is two. Hence, the total tensile strength is (10−2)×5256=42048N. Therefore, the total pulling strength is over than the total tensile strength.

[0105]FIG. 18 is a partially perspective plane view showing an arrangement of the butt portions 6 of the connecting section of the steel codes 5 of the third example of the invention. The positions of the butt portions 6 of the steel codes 5 are arranged within a plane of projection of the lug 4 or within a plane of projection of the core bar 3.

[0106] This example is an example of combination arrangement with four-shift lapping.

[0107]FIG. 19 is a partially perspective plane view showing an arrangement of the butt portions 6 of the connecting section of the steel codes 5 of the forth example of the invention. FIG. 20 is an explanatory view showing an arrangement of the steel codes 5 in FIG. 19.

[0108] Though this example is an example of combination arrangement with four-shift lapping as well as the third example, the positions of the butt portions 6 of the steel codes 5 are not arranged in the same line in the widthwise of the rubber crawler 1.

[0109] In ten steel codes 5 in one side of the steel code rows sandwiching the engaging holes 9, the adjoining steel codes 5 not overlapping with the steel codes extending from the opposite direction of the circumferential direction of the rubber crawler 1 among the steel codes forming the butt portions 6 within a space (K) from the middle of the core bar 3 (the width of the circumferential direction of the rubber crawler) to the middle of the adjoining core bar 3 (inside one interval of core bar) are arranged so as to be 25% or less of the whole steel codes 5.

[0110] The butt portions 6 within a space (K₁₋₂) from the middle of the core bar 3 ₁ to the middle of the adjoining core bar 3 ₂ are two, which are the butt portion 6 ₁ of the steel code 5 ₁ and the butt portion 6 ₆ of the steel code 5 ₆. These two steel codes 5 ₁ a, 5 ₆ a do not overlap with steel codes 5 ₂ b, 5 ₅ b, 5 ₇ b extending from the opposite direction of the circumferential direction of the rubber crawler 1 of the adjoining right and left steel codes at all. However, in this case, since a ratio to the whole steel codes (10 pieces) is 20% (2 pieces), trouble does not occur especially.

[0111] Besides, there are no butt portions within a space (K₂₋₃) from the middle of the core bar 3 ₂ to the middle of the adjoining core bar 3 ₃, and therefore, a ratio to the whole steel codes (10 pieces) is 0% (0 piece).

[0112] The ratios in spaces K₃₋₄, K₄₋₅, K₅₋₆, K₆₋₇, K₇₋₈, K₈₋₉ and K₉₋₁₀ are 20%, 0%, 20%, 0%, 20%, 0% and 20%, respectively. Namely, the ratios are set to 25% or less among all.

[0113] In this case, it is desirable that a range which the non-lapping steel codes are arranged so as to be 25% or less to the whole steel codes 5 is formed by a space between two core bars 3 adjoining against the whole planes of projection of two adjoining core bars 3 (for example, a space K′₁₋₂, a space K′₂₋₃). In this example, an arrangement of the butt portions 6 also satisfies this condition.

[0114]FIG. 21 is a partially perspective plane view showing an arrangement of the butt portions 6 of the connecting section of the steel codes 5 of the fifth example of the invention. This example is an example showing an arrangement combining the butt portions 6 with five-shift lapping.

[0115]FIG. 22 is a partially perspective plane view showing an arrangement of the butt portions 6 of the connecting section of the tensile strength bodies of the sixth example of the invention. FIG. 23 is an explanatory view for explaining an arrangement of the tensile strength bodies in FIG. 22, and shows an example of an arrangement combining the butt portions with one-shift lapping.

[0116] In these figures, the positions of the butt portions 6 ₁, 6 ₂ of the adjoining steel codes 5 ₁, 5 ₂ are shifted along the circumferential direction. The end 5 ₁ b of the steel code 5 ₁ and the end 5 ₂ a of the steel code 5 ₂ overlap each other along the circumferential direction, and are bonded to each other through adhesive rubber 7 ₁₋₂.

[0117] Besides, the end 5 ₂ a of the steel code 5 ₂ and the end 5 ₃ b of the steel code 5 ₃ overlap each other along the circumferential direction, and are bonded to each other through adhesive rubber 7 ₂₋₃.

[0118] The.end 5 ₃ a of the steel code 5 ₃ does not overlap with the end 5 ₂ b of the steel code 5 ₂ and the end 5 ₄ b of the steel code 5 ₄ extending from the opposite direction of the adjoining steel codes.

[0119] However, the end 5 ₃ a of the steel code 5 ₃ is bonded to the end 5 ₂ a of the steel code 5 ₂ through adhesive rubber 7′₂₋₃. Therefore, if the circumference L_(S)′ between the end 5 ₃ a of the steel code 5 ₃ and the end 5 ₁ b of the steel code 5 ₁ is the length with the puffing strength corresponding to the tensile strength of the steel code 5, an sufficient connecting efficiency can be obtained. The connecting efficiency is 83% in the one-shift lapping method of FIG. 22, and therefore, the connecting method is useful without special troubles.

[0120]FIG. 24 shows the seventh example of the invention, which is a partially perspective plane view of an arrangement of the butt portions of the connecting sections of the steel codes 5.

[0121] The rubber crawler 1 of the seventh example arranges pluralities of steel codes 5 as three rows of tensile strength bodies along the widthwise of the rubber crawler 1. In this case, the positions of the butt portions 6 of the adjoining steel codes 5 are shifted longitudinally circumferentially of the rubber crawler with respect to the positions of the butt portions 6 of the individual steel codes 5.

[0122]FIG. 25 shows the eighth example of the invention, which is a perspective view of the rubber crawler 1 using an arrangement of the butt portions 6 of the connecting section of the steel codes 5. FIG. 26A is a partially perspective plane view of an arrangement of the butt portions of the connecting sections of the steel codes 5, wherein pluralities of steel codes 5 are arranged as one row of tensile strength bodies along the widthwise of the rubber crawler 1. Besides, the rubber crawler 1 of the eighth example is a core bar less rubber crawler that no core bars 3 are embedded into the main body of the rubber crawler 1.

[0123]FIG. 26B is a partially perspective plane view showing another example of the eighth example shown in FIG. 26A, wherein the core bars 3 are embedded into the main body of the rubber crawler 1 of the eighth example.

[0124] The rubber crawler by the steel code connecting method of the invention and the rubber crawler by the conventional overlapping method are respectively mounted on a bending tester of FIG. 27, then carrying out a bending fatigue test. FIG. 35 is a diagram showing test results and the method of the rubber crawlers used in the bending fatigue test.

[0125] The bending test is carried out by mounting the rubber crawler on an eccentric sprocket and a driving sprocket of the bending tester and setting a spring so that 14.7 kW of tension is added to the rubber crawler. Besides, in this case, both bottom diameters of the eccentric sprocket and the driving sprocket are 224 mm.

[0126] As shown in FIG. 35, in the conventional rubber crawler, 165 mm separated from the front ends of the steel codes of the periphery side (treat side) among the belt-shaped overlapped steel codes by 560,000 times bending (970,000 times tension lodes). However, in the rubber crawler based on the invention, though 5,720,000 times bending (9,880,000 times tension lodes) were carried out, there was no problem. Here, the rubber crawler of the invention has durability of 10 times or more over the conventional one.

[0127] Furthermore, the invention can be carried out as follows.

[0128] (1) In the example which the tensile strength bodies are divided into two along the engaging part of the middle of the rubber crawler, and which two rows of tensile strength bodies are embedded in the rubber crawler, it is possible to arrange the butt portions of the tensile strength bodies in the connecting section of the right and left tensile strength body rows so as to be different in right and left as well as the bilateral-symmetry arrangement shown in the first example and the right and left same arrangement shown in the second example.

[0129] (2) Though the front edges of opposite ends of a tensile strength body are abutted against each other and connected together into an endless form in the above-mentioned examples, two or more tensile strength bodies may be connected based on the invention. In this case, two or more connecting sections are formed.

[0130] (3) The core bars embedded in the rubber crawler may be made from high molecular resin as well as metal. The material of a core bar is suitably chosen in consideration of required durability and economical efficiency. Besides, the core bar less rubber crawler in which no core bars are embedded may be used.

[0131] (4) It is possible to divide the tensile strength body rows into three rows or more and to embed them in a rubber crawler as well as the two rows of tensile strength bodies or the one row of the tensile strength body in the above-mentioned examples. Here, the one row of tensile strength body is mostly used in a rubber crawler with no engaging hole for a driving protrusion provided in the inner circumferential side, and is embedded in the middle of the widthwise of the rubber crawler.

[0132] Since the present invention has the above-mentioned construction, even in a sprocket and an idler winding section, there is no place which big shearing deformation such as occurs in the connecting section of the tensile strength bodies due to the conventional overlapping method occurs. Accordingly, even if unusual tension is added, the connecting section of the tensile strength bodies may not be destroyed easily. Therefore, the connecting section improves in durability, thereby forming a reliable rubber crawler.

[0133] Besides, while the connecting section length is restricted, the shift lapping length of the tensile strength body is designed so that the total pulling strength of the whole tensile strength bodies may be more than 80% of the total tensile strength of the remaining tensile strength bodies subtracted the number of the butt portions 6 within the predetermined interval of core bars with most butt portions from the number of the whole tensile strength bodies. Therefore, a practical and efficient connection is achieved, and a durable rubber crawler can be gained.

[0134] Moreover, since one position of the butt portions of the individual tensile strength bodies is shifted along the circumferential direction of the rubber crawler so as not to agree with the positions of the butt portions of the other tensile strength bodies, the inferior-durable butt portions do not concentrate on one place. Therefore, the connecting section can improve in durability.

[0135] In the configuration that the tensile strength bodies not overlapping with the tensile strength bodies extending from the opposite direction of the circumferential direction of the rubber crawler of the adjoining right and left tensile strength bodies are not concentratively arranged over 25% of the whole tensile strength bodies, it is not necessary to compensate the shortage of the intensity by increasing the tensile strength bodies or by using the tensile strength bodies with the high breaking strength. Therefore, a cost can be held down, and besides, the connecting section can improve in durability.

[0136] Furthermore, in the configuration that arranges the positions of the butt portions of the tensile strength bodies in a plane of projection of the lug or a plane of projection of the core bar, the ends of the tensile strength bodies are prevented from breaking through the rubber elastic body of the tread side. Therefore, the rubber crawler can improve in durability. 

1. A rubber crawler, comprising: rubber elastic body, and two rows of tensile strength bodies being embedded in said rubber elastic body; said two rows of tensile strength bodies comprising: pluralities of tensile strength bodies; said tensile strength bodies paralleled and arranged in a row widthwise of the rubber crawler along a circumferential direction thereof, and divided into two along a middle thereof wherein front edges of opposite ends 5 a, 5 b of the individual tensile strength bodies are abutted against each other and connected together into an endless form, and positions of butt portions 6 of not less than 80% of the tensile strength bodies 5 in a connecting section of each row of tensile strength bodies of two right and left rows of tensile strength bodies is such that positions of the butt portions 6 of adjoining tensile strength bodies 5 are shifted longitudinally circumferentially of a rubber crawler 1 with respect to a position of a butt portion 6 of a single tensile strength body
 5. 2. A rubber crawler, comprising: rubber elastic body, and two rows of tensile strength bodies being embedded in said rubber elastic body; said two rows of tensile strength bodies comprising: pluralities of tensile strength bodies; said tensile strength bodies paralleled and arranged in a row widthwise of the rubber crawler along a circumferential direction thereof and divided into two along a middle thereof wherein front edges of opposite ends 5 a, 5 b of the tensile strength bodies are abutted against each other and connected together into an endless form, and a position of a butt portion 6 of a single tensile strength body 5 in a connecting section of each row of tensile strength bodies of two right and left rows of tensile strength bodies is shifted longitudinally circumferentially of a rubber crawler 1 with respect to each position of butt portions 6 of adjoining tensile strength bodies
 5. 3. A rubber crawler as claimed in claim 1 or claim 2, wherein the positions of the butt portions 6 of the tensile strength bodies 5 in a connecting section of each row of tensile strength bodies are arranged so as to be 40% less than all tensile strength bodies 5 within a predetermined interval of the core bars in a circumferential direction of a rubber crawler
 1. 4. A rubber crawler as claimed in any claim 1 to 3, in said connecting section of each row of tensile strength bodies, wherein said butt portions 6 of the tensile strength bodies 5 within a space from a rubber crawler circumferential directional side edge of a core bar 3 to a rubber crawler circumferential directional side edge of an adjoining core bar 3, said space embedding no core bars, are 25% less than the number of all the tensile strength bodies
 5. 5. A rubber crawler as claimed in any claim 1 to 4, in said connecting section of each row of tensile strength bodies, wherein a total shift lapping length overlapping the tensile strength bodies 5 extending from one side of the circumferential direction of the adjoining tensile strength bodies 5 and the tensile strength bodies 5 extending from the other side is more than a length satisfying a relation that a total PS of pulling strength of all the tensile strength bodies 5 in rows of tensile strength bodies becomes 80% or more of a total tensile strength of remaining tensile strength bodies 5 subtracted the number CN of the butt portions in which the most many butt portions 6 exist within the predetermined interval of core bars from the number TN of all the tensile strength bodies arranged in a row.
 6. A rubber crawler as claimed in any claim 1 to 5, in said connecting section of each row of tensile strength bodies, wherein tensile strength bodies which the tensile strength bodies extending from one side never overlap with the tensile strength body extending from the opposite direction of the circumferential direction of the rubber crawler 1 adjoining tensile strength bodies 5 among the tensile strength bodies 5 forming the butt portions 6 within the predetermined interval from one core bar 3 to the adjoining core bar 3 are less than 25% of all the tensile strength bodies
 5. 7. A rubber crawler as claimed in any claim 1 to 6, in said connecting section of each row of tensile strength bodies, wherein the position of the butt portion 6 of the adjoining tensile strength body 5 is shifted in a circumferential direction of the rubber crawler 1 with respect to the position of the butt portion 6 of a single tensile strength body 5, the position of the butt portion 6 of the next adjoining tensile strength body 5 is shifted in the direction, and one after another the position of butt portions 6 of the individual adjoining tensile strength bodies is shifted in the direction, and 1 to 8 positions of the butt portions 6 are shifted in the direction one after another between a space from one side of the connecting section to the opposite side thereof with respect to the position of the butt portion 6 of a single tensile strength body
 5. 8. A rubber crawler as claimed in claim 7, wherein a group of 1 to 8 positions of the butt portions 6 shifted in the direction one after another between a space from one side to the opposite side of the connecting section of the rubber crawler with respect to the position of the butt portion 6 of a single tensile strength body 5 is combined with pluralities of groups in a forward direction or in an opposite direction thereof and arranged in the connecting section.
 9. A rubber crawler as claimed in any claim 1 to 8, wherein the position of the butt portion 6 of each tensile strength body 5 is arranged in a plane of projection of a lug 4 or in a plane of projection of a core bar
 3. 10. A rubber crawler as claimed in any claim 1 to 9, wherein a row of tensile strength bodies comprising pluralities of tensile strength bodies 5 paralleled and arranged in a row widthwise of the rubber crawler along the circumferential direction of the rubber crawler 1 in rubber elastic body 2 is made into a single row of tensile strength bodies without dividing into two along the middle of the rubber crawler.
 11. A rubber crawler as claimed in any claim 1 to 9, wherein a row of tensile strength bodies comprising pluralities of tensile strength bodies 5 paralleled and arranged in a row widthwise of the rubber crawler along the circumferential direction of the rubber crawler 1 in rubber elastic body 2 is made into pluralities of tensile strength body rows more than three. 